The present invention relates to a system for controlling an optical scanning exposure system suitable to the manufacture of cathode ray tubes and more particularly to a control system for storing information representative of the angle of incidence of a light beam at a matrix of points and scan rate information intermediate the points of the matrix and for applying the stored information to an optical scanning system to effect a proper rate and angle of scanning and deflection of a light beam which is imaged on a layer of photosensitive material affixed to the faceplate of a cathode ray tube.
At present, the most common technique of manufacturing cathode ray tubes and particularly color cathode ray tubes is a stationary or non-scanning technique. In this process, a layer of photosensitive material is affixed to the inner surface of the faceplate of the cathode ray tube, dusted with phosphor, and exposed at desired locations by a flood of light passing through the apertures of an adjacent apertured mask. The unexposed photosensitive material is then removed by well-known washing techniques while the exposed material is affixed to the faceplate.
As to control of the above-described exposure apparatus, the light source is usually an ultraviolet source whose output is directed through a small aperture and then dispersed to flood the entire apertured mask associated with the faceplate of the cathode ray tube. The intensity of the light appearing at the apertured mask, which is not necessarily uniform throughout the mask, is varied by varying the intensity of the source and by the use of a neutral density filter intermediate the light source and the apertured mask.
Additionally, it is well known that an electron beam in a cathode ray tube does not follow a straight-line trajectory due to the distributed magnetic fields associated with the operation of the cathode ray tube. In contrast, light beams do follow straight-line trajectories. To compensate for this discrepancy, a special contoured lens is normally disposed between the light source and the apertured mask. The lens is designed such that the light source appears to come from the correct location to cause the light rays to pass through the apertures of the mask at the same angle of incidence as would an electron beam in a cathode ray tube. Thus, the light beam passes through each aperture of the mask at an angle related to the angle of incidence of an electron beam passing through the same aperture.
Although widely used in fabricating cathode ray tubes, the above-mentioned technique is far from an ideal manufacturing process. Specifically, designing and fabricating the contoured lens is a costly and time-consuming procedure. The design of the lens is usually effected by a trial and error process which normally requires numerous repetitive attempts before a satisfactory result is obtained. Also, the neutral density filter is similarly designed requiring exhaustive trial and error attempts. Moreover, a lens and filter is required for each of the guns of a particular design and must be altered for changes in design of the guns, screens, curvature of the mask and numerous other parameters of the cathode ray tube structure.
Another known technique for manufacturing cathode ray tubes is what might be called a "scanning system" wherein a light beam from a light source is scanned across an apertured mask adjacent a layer of photosensitive material affixed to the faceplate of a cathode ray tube. The light passing through the apertures of the mask exposes the photosensitive material. This exposed photosensitive material remains affixed to the faceplate and the unexposed material is removed by washing in a well-known manner.
Although the above-mentioned broadly described exposure technique is suggested in a British patent specification No. 1,257,933 and in a U.S. patent issued to Grenen et al. bearing U.S. Pat. No. 3,876,425, any reference to apparatus for controlling the above-described exposure process is conspicuously absent. Specifically, each of the above patents is directed to the method of making a cathode ray tube by a scanning exposure technique rather than to a system for controlling an exposure or scanning process.